Door knocker



FIG. 1 is a front view of the door knocker illustrating the hingedly supported gavel-like striker and the decorative back plate;

FIG. 2 is a top view of the door knocker;

FIG. 3 is a side view of the door knocker taken from the left in FIG. 1;

FIG. 4 is a rear view of the decorative back plate, the rear view being a mirror image of the silhouette of the front view of the back plate. 

The ornamental design for a door knocker, substantially as shown and described. 